M Ebrahimi; H Kouhestani; M.A.A Mokhtari; M Feizi
Abstract
The Aqkand area is located at 48 km north of Zanjan and is a part of the Tarom subzone within the Western Alborz-Azerbaijan structural zone. Acidic rocks exposed in this area consist of Oligocene rhyolite-rhyodacite, perlite, pitchstone and ignimbrite. Rhyolites and rhyodacites are exposed as domes and ...
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The Aqkand area is located at 48 km north of Zanjan and is a part of the Tarom subzone within the Western Alborz-Azerbaijan structural zone. Acidic rocks exposed in this area consist of Oligocene rhyolite-rhyodacite, perlite, pitchstone and ignimbrite. Rhyolites and rhyodacites are exposed as domes and lava flows. Perlites are located at the lower parts of the rhyolitic-rhyodacitic domes. Geochemical investigations indicate calc-alkaline nature along with magmatic arc affinity for the studied rocks. These rocks are characterized by LREE-rich patterns with high LREE/HREE ratio and distinctive negative Eu anomaly. Positive anomalies of Rb, Pb and Th on the spider diagrams suggest continental crust involvement in the genesis and evolution of the parental magma. Based on tectonic setting discrimination diagrams, Aqkand acidic rocks are plotted in the post-collision tectonic setting. In overall petrographic, petrologic and geochemical evidence demonstrate that during the final stages of the continental collision, the thickened sub-continental lithosphere in the Alborz was delaminated and replaced by hot asthenospheric mantle. Rapid upwelling of hot asthenosphere gave rise to the partial melting of sub-continental lithosphere which produced the Oligocene basaltic rocks of the study area. Emplacement of basaltic magma in the upper part of the continental crust led to the partial melting of the crust and generation of the acidic magmas. Rapid cooling of acidic lavas led to the generation of glassy rocks such as obsidian which are changed to perlite in contact with meteoric and warm waters.
M.A.A Mokhtari; H Kouhestani; A Saeedi
Abstract
Aliabad Mousavi- Khanchy Cu occurrence is located in the Tarom area, 30 km east of Zanjan. Rock units exposed in this area consist of Eocene volcanic and volcano-sedimentary units (equal to Karaj Formation) which are intruded by Oligocene quartz-monzonitic plutons. In this area, Cu mineralization occurs ...
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Aliabad Mousavi- Khanchy Cu occurrence is located in the Tarom area, 30 km east of Zanjan. Rock units exposed in this area consist of Eocene volcanic and volcano-sedimentary units (equal to Karaj Formation) which are intruded by Oligocene quartz-monzonitic plutons. In this area, Cu mineralization occurs as Cu-bearing quartz veins and veinlets within the intermediate tuffs and andesitic lavas. Based on microscopic studies, ore minerals are include chalcopyrite with minor pyrite and oligist, and quartz and chlorite are present as gangue minerals at the Aliabad Mousavi- Khanchy Cu occurrence. The ore minerals show disseminated, vein and veinlets, breccia, open space filling and replacement textures. Alteration is restricted to the silicified and chloritic altered parts of the ore zones. Two stages of hypogene and supergene mineralization can be distinguished at the Aliabad Mousavi- Khanchy Cu occurrence. The hypogene stage of mineralization is progressed from disseminated crystals of pyrite and chalcopyrite within the tuffs and lavas (substage 1) to quartz- chalcopyrite- pyrite‒cemented veins and breccias (substage 2), individual or sets of quartz veins and veinlets (substage 3) and finally quartz- oligist veins and veinlets (substage 4). Malachite, azurite and Fe-hydroxides with veins and veinlets and open space filling textures are formed during supergene stage. REE pattern of the host rocks and the mineralized samples indicate that mineralized samples are enriched in REE. This signature may indicates high concentration of REE in ore-forming fluids and/or high W/R interaction at Aliabad Mousavi- Khanchy area. Enrichment of ore-forming elements (Cu, Pb, Zn) in ore zones is also specifies leaching of elements from altered host rocks to ore zones by ore-forming fluids. Characteristics of Aliabad Mousavi- Khanchy Cu occurrence are comparable with vein type of Cu deposits.